Archived 2017 topics: Cape Gannet (Morus capensis): uplist to Endangered?

Cape Gannet Morus capensis is a breeding endemic species of coastal southern Africa, breeding on 6 islands in total. These sites are evenly split between South Africa (Bird [Algoa Bay], Malgas and Bird [Lambert’s Bay] Islands) and Namibia (Ichaboae, Mercury and Possession Islands), although historically it is known to have bred at more sites (Kemper et al. 2007). The species is currently listed as Vulnerable under criteria A2acde+3cde+4acde; B2ab(iii,iv,v) on the basis of its breeding grounds being restricted to six small islands, while threats such as over-exploitation of its food sources by humans, exploitation for food, and pollution have led to rapid declines (see Kemper et al. 2007, BirdLife International 2017).

For a species to be listed as Vulnerable under criteria A2+3+4 the past/ongoing/future decline in the species needs to at least be suspected to fall in the range 30-49% over a three generation period. Recent data, however, shows that the species may in fact be declining at a faster rate than this and so may warrant listing as Endangered. Historically the global population numbered c.254,000 breeding pairs in 1956, which has subsequently decreased to c.249,000 pairs in 1968, c.179,000 in 1989 and c.145,000 pairs in 2005 (Crawford et al. 2007). The most recent population estimate is made up of 10,500 pairs at Ichaboae Island, 2,200 pairs on Mercury Island and 380 pairs on Possession Island (all in 2010) (Kemper 2015), with 81,000 pairs at Bird Island (Algoa Bay), 21,000 pairs at Malgas Island and 8,000 pairs at Bird Island (Lambert’s Bay) (in 2015) (Crawford et al. 2015 updated by R. Crawford in litt. 2016). This gives a global total of 123,080 pairs (roughly 123,000 pairs). While not necessarily a perfect representation of the global population in 2015, it is used as such for ease of trend calculations, and means trends calculated below may in fact be an underestimate of the rate of decline.

These trend calculations give an overall decline of 51.5% between 1956 and 2015, and with only minor extrapolation this would equate to a c.52.4% decline over 3 generations (60.6 years). When comparing the most recent population estimate to the 1968, 1989 and 2005 estimates the annual rates of decline are even higher, and if they were projected to continue into the future then the rate of decline over 3 generations would be c.60%. Therefore, rates of decline over 3 generations more than likely fall within the range of 50-79%, which would meet the threshold for listing as Endangered. Therefore, it is proposed that Cape Gannet be uplisted to Endangered under criteria A2acde+3cde+4acde.

We welcome any comments regarding this proposed uplisting.



BirdLife International. 2017. Species factsheet: Morus capensis. Downloaded from on 07/04/2017.

Crawford, R. J. M.; Dundee, B. L.; Dyer, B. M.; Klages, N. T. W.; Meyer, M. A.; Upfold, L. 2007. Trends in numbers of Cape gannets (Morus capensis), 1956/1957-2005/2006, with a consideration of the influence of food and other factors. ICES Journal of Marine Science 64(1): 169-177.

Crawford, R. J. M.; Makhado, A. B.; Whittington, P. A.; Randall, R. M.; Oosthuizen, W. H.; Waller, L. J. 2015. A changing distribution of seabirds in South Africa – the possible impact of climate and its consequences. Frontiers in Ecology and Evolution 3: 10, 1–10. doi: 10.3389/fevo.2015.000010.

Kemper, J. 2015. Cape Gannet. In: Simmons RE, Brown CJ, Kemper J (eds) Birds to watch in Namibia. Red, rare and endemic species. Ministry of Environment and Tourism, and Namibia Nature Foundation, Windhoek, pp 149–151.

Kemper, J.; Underhill, L. G.; Crawford, R. J. M.; Kirkman, S. P. 2007. Revision of the conservation status of seabirds and seals breeding in the Benguela Ecosystem. In: Kirkman, S. P. (ed.), Final Report of the BCLME (Benguela Current Large Marine Ecosystem), pp. 325-342.

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5 Responses to Archived 2017 topics: Cape Gannet (Morus capensis): uplist to Endangered?

  1. Dr Henning Winker (Department of Agriculture, Forestry and Fisheries, South African Government) and myself (Dr Richard Sherley, University of Exeter, UK) are in the process of developing a tool based on Bayesian state-space modelling which allows the user to assess the probability that an observed decline meets the IUCN criteria under A2 for listing in a threatened category. Given that the predicted decline was close to 50% in this case, and because we have long-standing collaborative relationships with the data holders for this species, we contacted Dr Rob Crawford (Department of Environmental Affairs, South Africa) and Dr Jessica Kemper (African Penguin Conservation Project, Namibia) to obtain the nest count data for Cape Gannets. The Bayesian state-space model fit to nests counts made between 1956 and 2016 at the species’ six breeding colonies in South Africa and Namibia indicates a decline of 51.5% (Bayesian 95% credible intervals: 39.5–62.5%) over three generations from a modelled population of 272,427 pairs for 1956 to 133,870 pairs for 2016. Overall, 61.6% of model iterations fell within the 50–79% decline band and 38.3% fell within the 30–49% band (Fig. 2). Thus, the balance of evidence from the model justifies the classification as Endangered under criteria A2 and we support the proposal to uplift the species.

    More information can be found here:

  2. Christina Hagen says:

    I agree with the suggestion to uplist to Endangered looking at the population numbers. And the additional analyses provided by Richard and Henning further suggest that it is justified.

  3. Lorien Pichegru says:

    I also agree with this update. I have worked on Malgas Island since 2004 and have seen the colony shrinking drastically, at a faster pace than counts seem to reveal. The threats weighing on Cape Gannets are not attended to appropriately at this stage, also due to a lack of accurate awareness, and it is likely that the population will continue decreasing in the coming years, further justifying the status of Endangered.

  4. Taryn Morris (BirdLife South Africa) says:

    Winker and Shirley have developed an advanced and robust assessment tool that clearly indicates uplisting of the Cape Gannet is required. The data are unequivocal and it is evident that this species needs our urgent attention.

    This tool has been supplied for assessment of various penguin species as well as other animal groups and I encourage the BirdLife Red List team to consider this approach as a standard tool for future listing assessments where the appropriate data exist. I strongly encourage the BirdLife Red List team to contact the authors for further engagement.

  5. Hannah Wheatley (BirdLife) says:

    Preliminary proposals

    Based on available information, our preliminary proposal for the 2017 Red List would be to adopt the proposed classifications outlined in the initial forum discussion.

    There is now a period for further comments until the final deadline of 4 August, after which the recommended categorisations will be put forward to IUCN.

    Please note that we will then only post final recommended categorisations on forum discussions where these differ from those in the initial proposal.

    The final 2017 Red List categories will be published on the BirdLife and IUCN websites in early December, following further checking of information relevant to the assessments by both BirdLife and IUCN.

Comments are closed.